Integrated circuits include many different components and are represented by many different designs. Examples of different designs are digital signal processors, central processing units, field-programmable gate arrays, memory, and so on. Non-volatile memory is one type of memory that preserves data with or without power. Manufacturers of non-volatile memory work continuously to improve the speed at which their memory operates and voltage shifters are one component in memory.
One problem with memory speed is found in the time it takes to shift lower input voltages to the higher voltages used by memory. Conventional voltage shifters shift relatively low voltage, for example a 1.8V logic signal, to a relatively high voltage, for example a 3.3V signal.
FIG. 1 is one example of a conventional voltage-level shifter 10. Shifter 10 receives a 1.8V signal at input 12 and “shifts” it to an output signal of 3.3V at output 14. Shifter 10 operates as follows.
Transistors 16 and 18 are thin-oxide, short-channel transistors that are inherently fast and small, but only tolerate voltage up to VDD from power supply 20. Transistors 16 and 18 are in an inverter configuration.
Transistors 22 and 24 are thick-oxide, long-channel transistors (relative to transistors 16 and 18) that can therefore tolerate higher voltage than transistors 16 and 18. Transistor 22 is connected to input 12 and receives the same input signal as transistors 18 and 16. Transistor 24, however, receives the inverted signal of input 12, because of the inverter configuration of transistors 16 and 18. Assuming input 12 is a high (VDD) voltage, then the gate of transistor 24 is deasserted (for example, a low voltage for N-channel transistors), while the gate of transistor 22 is asserted (for example, a high voltage for N-channel transistors).
Transistor 22 turns on, or begins conducting, because it is being asserted, while transistor 24 turns off because it's being deasserted. The effect of this is to turn on, or assert transistor 26 and turn off, or deassert transistor 28, which are both connected to power 30 at voltage level VCC, which is at 3.3V. Transistors 28 and 26 are thick-oxide, long, P-channel transistors (relative to transistors 16 and 18) that can therefore tolerate higher voltage than transistors 16 and 18. Because transistor 26 is on and conducting, while transistor 24 is off, output 14 is at VCC. Therefore the input voltage of 1.8V has been level-shifted to 3.3V. If input 12 goes to zero, then the opposite holds true, in that output 14 will go to zero as well.
One problem with voltage-level shifter 10 is that it is slow. In many electronic systems, memory being one example, rapidly functioning circuits are important to overall system performance.
Accordingly, what is needed is a faster voltage-level shifter. The present invention addresses such a need.